1. Field of the Invention
The present invention generally relates to a device for reading from and/or writing on digital data storage disks enabling optical reading and/or writing. Such disks are for example “CDs”, “DVDs”, “Bluerays”, or “HD-DVDs”.
2. Discussion of the Related Art
FIG. 1 is a known diagram of such a device. A mobile opto-electromechanical device 1 is placed above a disk 2 on a support 3 formed of two horizontal rails held on one side by a foot 4 laid next to disk 2. Opto-electromechanical device 1 is connected to a motherboard 5 by electric wires placed on a flexible strip 6.
The opto-electromechanical device structure is schematically shown to the bottom left of the drawing. Actuators 10 enable moving device 1 on the rails of support 3. A laser diode 11 emits light to read from or write on the disk. An image sensor 12 formed of a photodetector array continuously measures the intensity of the light reflected by the disk. Each photodetector of image sensor 12 provides an analog electric signal having a magnitude substantially proportional to the intensity of the light received by this photodetector. Actuators 10, laser diode 11, and image sensor 12 are connected to an electronic circuit 13 comprising the following elements. An amplifier 14 amplifies the analog electric signals provided by each of the photodetectors of image sensor 12 and transmits them to motherboard 5 in the form of a set of analog signals s. An amplifier 15 receives control signals cmd transmitted by the motherboard and, after amplification, transmits said signals to actuators 10. A regulation/amplification device 16 controls the light intensity of laser diode 11, the light intensity being small or variable according to whether a reading or a writing is performed. In a write phase, regulation/amplification device 16 receives a digital data signal D and varies the light intensity of laser diode 11 according to the type of bit to be written, the intensity being for example high to write a “1” and low to write a “0”, the writing of a bit at “1” causing a modification in the nature of the track portion corresponding to this bit and especially a modification in its reflective characteristics.
The motherboard receives or provides audio-visual signals for or from an apparatus such as a television or an audio system, and exchanges with opto-electromechanical device 1 previously-mentioned signals cmd, s, and D. Generally, motherboard 5 is a printed circuit on which are placed one or several integrated circuits. From a functional point of view, the motherboard can be divided into four main units. A “servo” unit 20 provides control signals cmd to actuators 10. A processing unit (proc RF) 21 processes the analog signals s originating from image sensor 12. Processing unit 21 provides a data signal d to a read unit R 23, which provides an audiovisual signal Se after demodulation and decoding. A write unit W receives an audiovisual signal Sr and performs a coding and a modulation of this signal, the coded and modulated signal being sent to opto-electromechanical device 1 in the form of a signal of digital data D to be written on disk 2.
Processing unit 21 analyzes the images provided by sensor 12 to detect four main elements. This analysis is performed in “analog” form with calculation means, and especially summing and subtracting means, operating from analog signals. The first two provided elements relate to the alignment of opto-electromechanical device 1 with respect to disk 2. These are address data @ indicating the disk area above which device 1 is placed, and data of alignment error Δ of device 1 with respect to the followed disk track, that is, too laterally offset from the track or again too close to or too far away from the track so that the light spot formed on the disk is not perfectly clear. Analog alignment data signals @ and Δ are transmitted to servo unit 20 which analyzes them and provides in return control signals cmd to the opto-electromechanical device to properly realign device 1 if necessary. Another element provided by processing unit 21 is an analog read data signal d which is demodulated and decoded by read unit R. The last element provided by processing unit 21 is a reference clock signal Ck known as a “wobble” signal. The period of reference clock Ck substantially corresponds to a multiple or to a sub-multiple of the duration of the passing under the sensor of a portion of the disk corresponding to a bit when the disk is rotating, or in other words, of the duration of overflight by the image sensor of a data bit written on disk 2. Reference clock signal Ck is transmitted to write unit W which transmits a digital data signal D to be written with a rate corresponding to the frequency of reference clock signal Ck.
As disk read and write speeds increase, more and more failures of the previously-described device can be observed. Such failures especially occur in devices using the most modern technologies known as “blue ray”. The encountered failures mainly are write errors.